In general, closure fastening devices for use in connection with plastic bags and the like are known. Furthermore, manufacturing methods for closure fastening devices made of plastic material are generally well known.
In operation, a closure fastening device for use in connection with a flexible container should be relatively easy to open from the outside, but relatively difficult to open from the inside. Generally, such a container can be used with its interior either under relatively high pressure or under relatively low pressure. The interior of a container is considered to be under relatively high pressure where the container is filled to its capacity, and under relatively low pressure when the container is only partially filled. The closure fastening device should provide a satisfactory seal for either condition, that is, the seal should be drip-proof and leak-proof.
Preferably, the closure fastening device should be suitable for economical manufacturing and should be relatively simple in design. In addition, to design should provide for variations in order to meet different needs. For example, it may be desirable to have a closure fastening device which is relatively more difficult to open from the inside than from the outside. In general, the closure fastening device, however, should always be relatively easy to close.
In addition, when the closure fastening device is employed with a container, the container may be made from a thermoplastic material and the closure device and sidewalls of the container can be made integrally by extrusion as a unitary piece or can be made as separate components which are subsequently permanently connected together.
One of the latest developments of such containers is a bag which can be used as a food storage container in a refrigerated or frozen condition as well as for heating and/or cooking food such as by placing the bag in hot water or in a microwave open. When used in a microwave oven, it is not unusual for such bags to encounter temperatures of 260.degree. F. to 300.degree. F., for example, such as when cooking meats. Even during the boiling of foods, such as in a metal pot, temperatures higher than 212.degree. F. are sometimes obtained above the water level such as near the rim of the pot necessitating better temperature resistance to softening or melting of the plastic bag than can be provided by the frequently used polyethylene resins. In order to overcome such problems at elevated temperatures, it is known that higher melting point resins may be employed which have higher stiffness moduli and therefore resist softening or melting. However, when such higher stiffness moduli resins are employed as the materials of construction for the closure device, the closure device resists bending and deflection, which are the most frequently used means of occlusion and de-occlusion of interlocking closure devices made from flexible resins such as polyethylene.
Another requirement of plastic food containers is the provision of an interlocking closure device which is drip-proof and leak-proof even when made from thermoplastic materials having the aforementioned properties of high stiffness moduli and resistance to elevated temperatures. Copending application Ser. No. 774400 filed contemporaneously herewith, titled Single Hinge Interlocking Closure Profile Configuration, commonly assigned to the present assignee, describes an interlocking closure device which meets the aforementioned temperature criteria and has the advantage of ease of occlusion and de-occlusion from outside forces while strongly resisting inside opening forces. However, this closure device is dripless when the container is filled with liquids only when the closure device is very carefully extruded. Accordingly, the direct and associated costs of manufacturing the single hinge type of interlocking closure device are quite high.
Therefore, it would be highly desirable to obtain an interlocking closure device having relative ease of occlusion and de-occlusion, wherein the interlocking closure device is resistant to elevated temperatures, the closure device may be manufactured with ample tolerance latitude, and wherein a container equipped with the interlocking closure device is leak-proof and drip-proof at the various temperatures and conditions of use.